Method and apparatus for assessing left ventricular function and optimizing cardiac pacing intervals based on left ventricular wall motion

ABSTRACT

A system and method for monitoring left ventricular (LV) lateral wall motion and for optimizing cardiac pacing intervals based on left ventricular lateral wall motion is provided. The system includes an implantable or external cardiac stimulation device in association with a set of leads including a left ventricular epicardial or coronary sinus lead equipped with a motion sensor electromechanically coupled to the lateral wall of the left ventricle. The device receives and processes wall motion sensor signals to determine a signal characteristic indicative of systolic LV lateral wall motion or acceleration. An automatic pacing interval optimization method evaluates the LV lateral wall motion during varying pacing interval settings, including atrial-ventricular intervals and inter-ventricular intervals and selects the pacing interval setting(s) that correspond to LV lateral wall motion associated with improved cardiac synchrony and hemodynamic performance.

FIELD OF THE INVENTION

[0001] The present invention relates generally to implantable medicaldevices for monitoring or treating a cardiac abnormalities and moreparticularly to a device and method for delivering cardiac pacingimpulses at inter-chamber intervals that are optimized based on leftventricular wall motion monitoring.

BACKGROUND OF THE INVENTION

[0002] Evaluation of left ventricular function is of interest for bothdiagnostic and therapeutic applications. During normal cardiac function,the left atrium, the left ventricle, and the right ventricle observeconsistent time-dependent relationships during the systolic(contractile) phase and the diastolic (relaxation) phase of the cardiaccycle. During cardiac dysfunction associated with pathologicalconditions or following cardiac-related surgical procedures, thesetime-dependent mechanical relationships are often altered. Thisalteration, when combined with the effects of weakened cardiac muscles,reduces the ability of the ventricle to generate contractile strengthresulting in hemodynamic insufficiency.

[0003] Ventricular dyssynchrony following coronary artery bypass graft(CABG) surgery is a problem encountered relatively often, requiringpost-operative temporary pacing. Atrio-biventricular pacing has beenfound to improve post-operative hemodynamics following such procedures.

[0004] Ventricular resynchronization therapy has been clinicallydemonstrated to improve indices of cardiac function in patientssuffering from congestive heart failure. Cardiac pacing may be appliedto one or both ventricles or multiple heart chambers, including one orboth atria, to improve cardiac chamber coordination, which in turn isthought to improve cardiac output and pumping efficiency. Clinicalfollow-up of patients undergoing resynchronization therapy has shownimprovements in hemodynamic measures of cardiac function, leftventricular volumes, and wall motion. However, not all patients respondfavorably to cardiac resynchronization therapy. Physicians arechallenged in selecting patients that will benefit and in selecting theoptimal pacing intervals applied to resynchronize the heart chambercontractions.

[0005] Selection of atrial-ventricular (A-V) and inter-ventricular (V-V)pacing intervals may be based on echocardiographic studies performed todetermine the settings resulting in the best hemodynamic response.However, this approach provides only an open-loop method. Afterevaluating the hemodynamic effect of varying combinations of pacingintervals, a physician must manually select and program the desiredparameters and assume that the patient's device optimal settings remainunchanged until a subsequent re-optimization visit. Automated methodsfor selecting pacing intervals during multi-chamber pacing have beenproposed. A four-chamber pacing system that includes impedance sensingfor determining the timing of right heart valve closure or rightventricular contraction and adjusting the timing of delivery of leftventricular pace pulses is generally disclosed in U.S. Pat. No.6,223,082 issued to Bakels, et al., incorporated herein by reference inits entirety. Programmable coupling intervals selected so as to provideoptimal hemodynamic benefit to the patient in an implantablemultichamber cardiac stimulation device are generally disclosed in U.S.Pat. No. 6,473,645 issued to Levine, incorporated herein by reference inits entirety.

[0006] Doppler tissue imaging has been used clinically to evaluatemyocardial shortening rates and strength of contraction. This rate ofcontraction has been investigated as a determinant of clinical health ofthe ventricle. Doppler tissue imaging has also been used to investigatecoordination between septal and lateral wall motion for predicting whichpatients are likely to benefit from cardiac resynchronization therapy.Evidence suggests patient response is dependent on the degree ofventricular synchrony before and after therapy. Doppler tissue imagingstudies have shown that the left ventricular mid to mid-basal segmentsshow the greatest improvement in shortening following cardiacresynchronization therapy. Detection and monitoring of left ventricularwall motion, therefore, would be useful in optimizing cardiacresynchronization therapy.

[0007] Implantable sensors for monitoring heart wall motion have beendescribed. A sensor implanted in the heart mass for monitoring heartfunction by monitoring the momentum or velocity of the heart mass isgenerally disclosed in U.S. Pat. No. 5,454,838 issued to Vallana et al.A catheter for insertion into the ventricle for monitoring cardiaccontractility having an acceleration transducer at or proximate thecatheter tip is generally disclosed in U.S. Pat. No. 6,077,236 issued toCunningham. Implantable leads incorporating accelerometer-based cardiacwall transducers are generally disclosed in U.S. Pat. No. 5,628,777issued to Moberg, et al. A device for sensing natural heart accelerationis generally disclosed in U.S. Pat. No. 5,693,075, issued to Plicchi, etal. A system for myocardial tensiometery including a tensiometricelement disposed at a location subject to bending due to cardiaccontractions is generally disclosed in U.S. Pat. No. 5,261,418 issued toFerek-Petric et al. All of the above-cited patents are herebyincorporated herein by reference in their entirety.

[0008] Detection of peak endocardial wall motion in the apex of theright ventricle for optimizing A-V intervals has been validatedclinically. A system and method for using cardiac wall motion sensorsignals to provide hemodynamically optimal values for heart rate and AVinterval are generally disclosed in U.S. Pat. No. 5,549,650 issued toBornzin, et al., incorporated herein by reference in its entirety. Acardiac stimulating system designed to automatically optimize both thepacing mode and one or more pacing cycle parameters in a way thatresults in optimization of a cardiac performance parameter, includingfor example heart accelerations, is generally disclosed in U.S. Pat. No.5,540,727, issued to Tockman, et al.

[0009] A need remains, however, for providing a device and method formonitoring left ventricular wall motion and for selecting optimalcardiac pacing intervals that produce the greatest improvement in leftventricular wall motion during multi-chamber or biventricular pacingdelivered to improve heart chamber synchronization, chronically oracutely. Improved left ventricular wall motion is expected to reflect animprovement in cardiac chamber synchrony and generally result in a netimprovement in cardiac efficiency.

SUMMARY OF THE INVENTION

[0010] The present invention provides a method and apparatus forassessing left ventricular function and optimizing cardiac pacingintervals based on detection of left ventricular wall motion. In oneembodiment, the present invention is realized in a cardiacresynchronization system that includes an implantable multi-chamberpulse generator and associated lead system wherein a left ventricularcoronary sinus lead or left ventricular epicardial lead is provided witha sensor for detecting left ventricular wall motion. In an alternativeembodiment, a temporary, external pulse generator is coupled totemporary pacing leads including a left ventricular temporary pacinglead equipped with a wall motion sensor. For each embodiment of thepresent invention, in addition to the pulse generator appropriatedefibrillator circuitry may be employed in electrical communication tosuitable

[0011] In a preferred embodiment, the wall motion sensor is anaccelerometer, which may be a uniaxial, biaxial, or triaxialaccelerometer. Alternatively, the wall motion sensor may be provided asother types of piezoelectric sensors, optical sensors, Hall-effect typesensors, capacitive, resistive, inductive or any other type of sensorcapable of generating a signal proportional to left-ventricular freewall motion or acceleration. A left ventricular wall motion sensor ispreferably placed in or proximate the mid- or mid-basal left ventricularfree wall segments.

[0012] The implantable or external pulse generator receives andprocesses the wall motion sensor signal during an automated testingroutine, which includes application of varying resynchronization pacingintervals, including atrial-ventricular and/or ventricular-ventricularintervals. Signal processing is performed to time-average the wallmotion signal and derive averaged signal parameters as indices of leftventricular free wall motion or acceleration. The pacing intervalsproducing the greatest improvement in left ventricular wall motion,based on the wall motion sensor data, can be automatically selected fordelivering cardiac resynchronization therapy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1A depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardialleads.

[0014]FIG. 1B depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardial leadsand an additional left ventricular epicardial lead equipped with a wallmotion sensor.

[0015]FIG. 2 is a schematic block diagram of the multi-chamber pacemakerof FIG. 1A capable of delivering a resynchronization therapy andprocessing left ventricular wall motion sensor signal input.

[0016]FIG. 3 depicts an alternative, epicardial lead system coupled to apatient's heart.

[0017]FIG. 4 is a flow chart providing an overview of a method foroptimizing cardiac pacing intervals based on monitoring LV wall motion.

[0018]FIG. 5 is a flow chart summarizing steps included in a method fordetermining an optimal AV interval based on left ventricular wall motionfor use in the method of FIG. 4.

[0019]FIG. 6 is a graph of sample, experimental LV wall motion datacollected from an accelerometer during atrio-biventricular pacing atvarying A-V intervals and simultaneous right and left ventricular pacing(V-V interval set to 0 ms).

[0020]FIG. 7 is a flow chart summarizing steps included in a method fordetermining an optimal V-V interval based on left ventricular wallmotion for use the method FIG. 4.

[0021]FIG. 8 is a graph of sample, experimental LV wall motion datacollected from an accelerometer during atrio-biventricular pacing atvarying V-V intervals and an A-V interval previously optimized to 130ms.

[0022]FIG. 9 is a flow chart summarizing steps included in a method formonitoring left ventricular function based on lateral wall motion.

DETAILED DESCRIPTION OF THE INVENTION

[0023] As indicated above, the present invention is directed towardproviding a method and apparatus for evaluating left ventricularfunction and selecting cardiac pacing intervals for the purposes ofrestoring normal ventricular synchrony based on monitoring leftventricular free wall motion. The present invention is useful inoptimizing atrial-ventricular and inter-ventricular pacing intervalsduring chronic resynchronization therapy used for treating heartfailure. The present invention is also useful in selecting pacingparameters used during temporary pacing applied for treatingpost-operative ventricular dyssynchrony. As such, the present inventionmay be embodied in an implantable cardiac pacing system including a dualchamber or multichamber pacemaker and associated set of leads.Alternatively, the present invention may be embodied in a temporarypacing system including an external pacing device with associatedtemporary pacing leads.

[0024]FIG. 1A depicts an exemplary implantable, multi-chamber cardiacpacemaker 14 in which the present invention may be implemented. Themulti-chamber pacemaker 14 is provided for restoring ventricularsynchrony by delivering pacing pulses to one or more heart chambers asneeded to control the heart activation sequence. The pacemaker 14 isshown in communication with a patient's heart 10 by way of three leads16, 32 and 52. The heart 10 is shown in a partially cut-away viewillustrating the upper heart chambers, the right atrium (RA) and leftatrium (LA), and the lower heart chambers, the right ventricle (RV) andleft ventricle (LV), and the coronary sinus (CS) extending from theopening in the right atrium laterally around the atria to form the greatcardiac vein 48, which branches to form inferior cardiac veins.

[0025] The pacemaker 14, also referred to herein as the “implantablepulse generator” or “IPG,” is implanted subcutaneously in a patient'sbody between the skin and the ribs. Three transvenousendocardial leads16, 32 and 52 connect the IPG 14 with the RA, the RV and the LV,respectively. Each lead has at least one electrical conductor andpace/sense electrode. A remote indifferent can electrode 20 is formed aspart of the outer surface of the housing of the IPG 14. The pace/senseelectrodes and the remote indifferent can electrode 20 can beselectively employed to provide a number of unipolar and bipolarpace/sense electrode combinations for pacing and sensing functions.

[0026] The depicted bipolar endocardial RA lead 16 is passed through avein into the RA chamber of the heart 10, and the distal end of the RAlead 16 is attached to the RA wall by an attachment mechanism 17. Thebipolar endocardial RA lead 16 is formed with an in-line connector 13fitting into a bipolar bore of IPG connector block 12 that is coupled toa pair of electrically insulated conductors within lead body 15 andconnected with distal tip RA pace/sense electrode 19 and proximal ringRA pace/sense electrode 21 provided for achieving RA pacing and sensingof RA electrogram (EGM) signals.

[0027] Bipolar, endocardial RV lead 32 is passed through the RA into theRV where its distal ring and tip RV pace/sense electrodes 38 and 40 arefixed in place in the apex by a conventional distal attachment mechanism41. The RV lead 32 is formed with an in-line connector 34 fitting into abipolar bore of IPG connector block 12 that is coupled to a pair ofelectrically insulated conductors within lead body 36 and connected withdistal tip RV pace/sense electrode 40 and proximal ring RV pace/senseelectrode 38 provided for RV pacing and sensing of RV EGM signals. RVlead 32 may optionally include a RV wall motion sensor 60. RV wallmotion sensor 60 may be positioned into or proximate the RV apex fordetecting motion or acceleration of the RV apical region. Implantationof an acceleration sensor in the right ventricle is generally disclosedin the above-cited U.S. Pat. No. 5,693,075 issued to Plicchi, et al.

[0028] In this illustrated embodiment, a unipolar, endocardial LV CSlead 52 is passed through the RA, into the CS and further into a cardiacvein to extend the distal LV CS pace/sense electrode 50 alongside the LVchamber to achieve LV pacing and sensing of LV EGM signals. The LV CSlead 52 is coupled at the proximal end connector 54 fitting into a boreof IPG connector block 12. A small diameter unipolar lead body 56 isselected in order to lodge the distal LV CS pace/sense electrode 50deeply in a cardiac vein branching from the great cardiac vein 48.

[0029] In accordance with the present invention, the coronary sinus lead52 is provided with a sensor 62 capable of generating a signalproportional to the motion of the left ventricular free wall. Sensor 62is preferably embodied as a uniaxial, biaxial, or triaxial accelerometercontained in a capsule of a relatively small size and diameter such thatit may be included in a coronary sinus lead without substantiallyincreasing the lead diameter or impairing the ability to steer the leadto a left ventricular pacing and sensing site. Radial information maynot be as valuable in assessing LV wall motion and optimizing pacingintervals as longitudinal information, therefore, a uniaxialaccelerometer may be adequate for these purposes. Sensor 62 mayalternatively be provided as another type of sensor such as an optical,acoustical, or Hall effect sensor or a sensor having piezoelectric,inductive, capacitive, resistive, or other elements which produce avariable signal proportional to left ventricular wall motion oracceleration. Sensor 62 is preferably located on CS lead 52 such thatwhen CS lead 52 is positioned for LV pacing and sensing, sensor 62 islocated approximately over the left ventricular free wall mid-lateral tomid-basal segments. The depicted positions of the leads and electrodesshown in FIG. 1A in or about the right and left heart chambers areapproximate and merely exemplary. For example, a left ventricular wallmotion sensor 62 may alternatively be located on CS lead 52 such thatsensor 62 is positioned in the coronary sinus, in the great cardiacvein, or in any accessible inferior cardiac vein. Furthermore, it isrecognized that alternative leads and pace/sense electrodes that areadapted for placement at pacing or sensing sites on or in or relative tothe RA, LA, RV and LV may be used in conjunction with the presentinvention.

[0030] In a four chamber embodiment, LV CS lead 52 could bear a proximalLA CS pace/sense electrode positioned along the lead body to lie in thelarger diameter coronary sinus adjacent the LA for use in pacing the LAor sensing LA EGM signals. In that case, the lead body 56 would encasean insulated lead conductor extending proximally from the more proximalLA CS pace/sense electrode(s) and terminating in a bipolar connector 54.

[0031]FIG. 1B depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardial leadsand an additional left ventricular epicardial lead equipped with wallmotion sensor 62. Patients may already be implanted with a transvenouslead system that includes a coronary sinus lead 52 that is not equippedwith a wall motion sensor. Such patients may benefit from the placementof an epicardial lead 64 equipped with wall motion sensor 62 coupled toIPG 14 via a connector 66 so as to provide an LV wall motion signal foruse in a closed-loop feedback system for providing resynchronizationtherapy at optimal pacing intervals.

[0032] Epicardial lead 64 is provided with a fixation member 63 whichmay serve additionally as a pacing and/or sensing electrode. In somecases, an epicardial lead may be preferred over a coronary sinus leaddue to the difficulty in advancing a coronary sinus lead into a cardiacvein over the LV free wall. Placement of a coronary sinus lead can be acumbersome task due to the tortuosity of the cardiac veins. Therefore,it may be desirable, at least in some patients, to provide an epicardiallead that can be positioned on the LV lateral wall for pacing, EGMsensing and wall motion monitoring, eliminating the need for a coronarysinus lead. Alternatively, it may be desirable to deploy a smalldiameter coronary sinus lead for LV pacing and EGM sensing with aseparate LV epicardial lead positioned for sensing LV lateral wallmotion.

[0033] The embodiment generally shown in FIG. 1B is particularlyadvantageous for use in selecting resynchronization therapy pacingsites. With epicardial lead 64 fixed at a desired location for assessingLV wall motion, the effect of pacing at different locations in one ormore heart chambers can be evaluated by deploying the transvenous pacingleads 16,32 and 52 to different locations. In particular, coronary sinuslead 52 may be advanced to different locations until an optimal locationis identified based on analysis of the signal from LV wall motion sensor62. By providing wall motion sensor 62 on a separate, epicardial lead64, the position of pacing electrode 50, provided on coronary sinus lead52, may be adjusted independently of sensor 62. If the position ofpacing electrode 50 needs adjusting, wall motion sensor 62 may remainfixed at a desired LV lateral wall location thereby allowing comparisonsto be made between measurements repeated at the same location fordifferent pacing intervals and/or pacing sites.

[0034]FIG. 2 is a schematic block diagram of an exemplary multi-chamberIPG 14, such as that shown in FIG. 1A or 1B, that provides delivery of aresynchronization therapy and is capable of processing left ventricularwall motion sensor signal input. The IPG 14 is preferably amicroprocessor-based device. Accordingly, microprocessor-based controland timing system 102, which varies in sophistication and complexitydepending upon the type and functional features incorporated therein,controls the functions of IPG 14 by executing firmware and programmedsoftware algorithms stored in associated RAM and ROM. Control and timingsystem 102 may also include a watchdog circuit, a DMA controller, ablock mover/reader, a CRC calculator, and other specific logic circuitrycoupled together by on-chip data bus, address bus, power, clock, andcontrol signal lines in paths or trees in a manner known in the art. Itwill also be understood that control and timing functions of IPG 14 canbe accomplished with dedicated circuit hardware or state machine logicrather than a programmed microcomputer.

[0035] The IPG 14 includes interface circuitry 104 for receiving signalsfrom sensors and pace/sense electrodes located at specific sites of thepatient's heart chambers and delivering cardiac pacing to control thepatient's heart rhythm and resynchronize heart chamber activation. Theinterface circuitry 104 therefore includes a therapy delivery system 106intended for delivering cardiac pacing impulses under the control ofcontrol and timing system 102. Delivery of pacing pulses to two or moreheart chambers is controlled in part by the selection of programmablepacing intervals, which can include atrial-atrial (A-A),atrial-ventricular (A-V), and ventricular-ventricular (V-V) intervals.

[0036] Physiologic input signal processing circuit 108 is provided forreceiving cardiac electrogram (EGM) signals for determining a patient'sheart rhythm. Physiologic input signal processing circuit 108additionally receives signals from left ventricular wall motion sensor62, and optionally RV wall motion sensor 60, and processes these signalsand provides signal data to control and timing system 102 for furthersignal analysis. For purposes of illustration of the possible uses ofthe invention, a set of lead connections are depicted for makingelectrical connections between the therapy delivery system 106 and theinput signal processing circuit 108 and sets of pace/sense electrodes,wall motion sensors, and any other physiological sensors located inoperative relation to the RA, LA, RV and LV.

[0037] Control and timing system 102 controls the delivery of bi-atrial,bi-ventricular, or multi-chamber cardiac pacing pulses at selectedintervals intended to improve heart chamber synchrony. The delivery ofpacing pulses by IPG 14 may be provided according to programmable pacingintervals, such as programmable conduction delay window times asgenerally disclosed in U.S. Pat. No. 6,070,101 issued to Struble et al.,incorporated herein by reference in its entirety, or programmablecoupling intervals as generally disclosed in above-cited U.S. Pat. No.6,473,645 issued to Levine. Selection of the programmable pacingintervals is preferably based on a determination of left ventricularwall motion derived from sensor 62 signals as will be described ingreater detail below.

[0038] The therapy delivery system 106 can optionally be configured toinclude circuitry for delivering cardioversion/defibrillation therapy inaddition to cardiac pacing pulses for controlling a patient's heartrhythm. Accordingly, leads in communication with the patient's heartcould additionally include high-voltage cardioversion or defibrillationshock electrodes.

[0039] A battery 136 provides a source of electrical energy to powercomponents and circuitry of IPG 14 and provide electrical stimulationenergy for delivering electrical impulses to the heart. The typicalenergy source is a high energy density, low voltage battery 136 coupledwith a power supply/POR circuit 126 having power-on-reset (POR)capability. The power supply/POR circuit 126 provides one or more lowvoltage power (Vlo), the POR signal, one or more reference voltage(VREF) sources, current sources, an elective replacement indicator (ERI)signal, and, in the case of a cardioversion/defibrillator capabilities,high voltage power (Vhi) to the therapy delivery system 106. Not all ofthe conventional interconnections of these voltages and signals areshown in FIG. 2.

[0040] Current electronic multi-chamber pacemaker circuitry typicallyemploys clocked CMOS digital logic ICs that require a clock signal CLKprovided by a piezoelectric crystal 132 and system clock 122 coupledthereto as well as discrete components, e.g., inductors, capacitors,transformers, high voltage protection diodes, and the like that aremounted with the ICs to one or more substrate or printed circuit board.In FIG. 2, each CLK signal generated by system clock 122 is routed toall applicable clocked logic via a clock tree. The system clock 122provides one or more fixed frequency CLK signal that is independent ofthe battery voltage over an operating battery voltage range for systemtiming and control functions and in formatting uplink telemetry signaltransmissions in the telemetry I/O circuit 124.

[0041] The RAM registers included in microprocessor-based control andtiming system 102 may be used for storing data compiled from sensed EGMsignals, wall motion signals, and/or relating to device operatinghistory or other sensed physiologic parameters for uplink telemetrytransmission upon receipt of a retrieval or interrogation instructionvia a downlink telemetry transmission. Criteria for triggering datastorage can be programmed via down linked instructions and parametervalues. Physiologic data, including wall motion data, may be stored on atriggered or periodic basis or by detection logic within the physiologicinput signal processing circuit 108. In some cases, the IPG 14 includesa magnetic field sensitive switch 130 that closes in response to amagnetic field, and the closure causes a magnetic switch circuit 120 toissue a switch closed (SC) signal to control and timing system 102 whichresponds in a magnet mode. For example, the patient may be provided witha magnet 116 that can be applied over the subcutaneously implanted IPG14 to close switch 130 and prompt the control and timing system todeliver a therapy and/or store physiologic data. Event related data,e.g., the date and time and current pacing parameters, may be storedalong with the stored physiologic data for uplink telemetry in a laterinterrogation session.

[0042] Uplink and downlink telemetry capabilities are provided to enablecommunication with either a remotely located external medical device ora more proximal medical device on or in the patient's body. Stored EGM,or LV wall motion data as well as real-time generated physiologic dataand non-physiologic data can be transmitted by uplink RF telemetry fromthe IPG 14 to the external programmer or other remote medical device 26in response to a downlink telemetered interrogation command. As such, anantenna 128 is connected to radio frequency (RF) transceiver circuit 124for the purposes of uplink/downlink telemetry operations. Telemeteringboth analog and digital data between antenna 128 and an external device26, also equipped with an antenna 118, may be accomplished usingnumerous types of telemetry systems known in the art for use inimplantable devices.

[0043] The physiologic input signal processing circuit 108 includes atleast one electrical signal amplifier circuit for amplifying, processingand in some cases detecting sense events from characteristics of theelectrical sense signal or sensor output signal. The physiologic inputsignal processing circuit 108 may thus include a plurality of cardiacsignal sense channels for sensing and processing cardiac signals fromsense electrodes located in relation to a heart chamber. Each suchchannel typically includes a sense amplifier circuit for detectingspecific cardiac events and an EGM amplifier circuit for providing anEGM signal to the control and timing system 102 for sampling, digitizingand storing or transmitting in an uplink transmission. Atrial andventricular sense amplifiers include signal processing stages fordetecting the occurrence of a P-wave or R-wave, respectively andproviding an atrial sense or ventricular sense event signal to thecontrol and timing system 102. Timing and control system 102 responds inaccordance with its particular operating system to deliver or modify apacing therapy, if appropriate, or to accumulate data for uplinktelemetry transmission in a variety of ways known in the art. Thus theneed for pacing pulse delivery is determined based on EGM signal inputaccording to the particular operating mode in effect. The intervals atwhich pacing pulses are delivered are preferably determined based on anassessment of LV wall motion data.

[0044] As such, input signal processing circuit 108 further includessignal processing circuitry for receiving, amplifying, filtering,averaging, digitizing or otherwise processing the LV wall motion sensorsignal. If additional wall motion sensors are included in the associatedlead system, for example a RV wall motion sensor, additional wall motionsignal processing circuitry may be provided as needed. Wall motionsignal processing circuitry is further provided for detection and/ordetermination of one or more wall motion signal characteristics such asmaximum and minimum peak amplitudes, slopes, integrals, or other time orfrequency domain signal characteristics that may be used as indices ofwall motion or correlates to hemodynamic performance. Such wall motionsignal characteristic values determined from an LV wall motion sensorsignal are made available to control and timing system 102 via LV MOTIONsignal line for use in algorithms performed for identifying pacingintervals producing optimal LV wall motion. If an RV wall motion sensoris present, an additional RV MOTION signal line provides RV wall motionsignal data to control and timing system 102.

[0045]FIG. 3 depicts an alternative, epicardial lead system coupled to apatient's heart. Epicardial leads may be used in conjunction with eitherchronically implantable or temporary external pacing systems. In theembodiment shown, RV epicardial lead 80 is shown fixed via an activefixation electrode 82 near the apex of the RV such that the activefixation electrode 82 is positioned in contact with the RV epicardialtissue for pacing and sensing in the right ventricle. RV epicardial lead80 may optionally be equipped with an RV wall motion sensor 84 fordetecting motion or acceleration of the RV apical region. LV epicardiallead 70 is shown fixed via an active fixation electrode 72 in the LVfree wall such that active fixation electrode 72 is positioned incontact with the LV epicardial tissue for pacing and sensing in the leftventricle. LV epicardial lead 70 is equipped with a wall motion sensor74 for detecting motion or acceleration of the LV free wall. Epicardiallead systems may further include epicardial RA and/or LA leads. Variouscombinations of epicardial and transvenous endocardial leads are alsopossible for use with biventricular or multichamber cardiac stimulationsystems.

[0046] In FIG. 3, RV and LV epicardial leads 70 and 80 are shown coupledto an external, temporary cardiac pacing device 90. External pacingdevice 90 is preferably a microprocessor controlled device includingmicroprocessor 96 with associated RAM and ROM for storing and executingfirmware and programmable software for controlling the delivery ofpacing pulses to LV and RV pace/sense electrodes 72 and 82. Externaldevice 90 receives signals from and delivers electrical pulses to LV andRV pace/sense electrodes 72 and 82 via conductors included in LVepicardial lead body 76 and RV epicardial lead body 86. EGM signals, LVwall motion signals, and optionally RV wall motion signals are receivedas input to input signal processing circuitry 94. Pacing impulses aredelivered by output circuitry 92 as needed, based on sensed EGM signals,at intervals determined based on signals received from LV wall motionsensor 74 as will be described in greater detail below. It is recognizedthat an epicardial lead system such as that shown in FIG. 3 thatincludes an LV wall motion sensor and optionally an RV wall motionsensor may alternatively be used in conjunction with an implantablepacing system, such as the multi-chamber system described above andshown in FIGS. 1 and 2.

[0047] External device 90 of FIG. 3 and implantable device 14 of FIGS. 1and 2 are shown to provide both sensing/monitoring and pacing deliverycapabilities. Certain device features may be enabled or disabled asdesired. For example, monitoring of LV wall motion without delivery of apacing therapy may be desired. LV wall motion sensor signal data maytherefore be received, processed and stored by an implantable orexternal device for later analysis and review by a clinician.

[0048]FIG. 4 is a flow chart providing an overview of a method foroptimizing cardiac pacing intervals based on monitoring LV wall motion.Method 200 begins at step 205 by monitoring LV wall motion. Preferably awall motion sensor is implanted in or proximate to the LV free wall asdescribed above. More preferably, an LV wall motion signal is obtainedfrom an accelerometer located on a coronary sinus lead advanced suchthat the accelerometer is positioned in a cardiac vein over themid-lateral, mid-basal or basal segment of the left ventricular freewall.

[0049] At step 210, an optimal A-V interval is determined if the pacingmode is an atrioventricular or atrio-biventricular mode. Depending onthe dual chamber or multichamber pacing system being used, a right A-Vinterval or a left A-V interval or both may be determined. For theembodiment shown in FIG. 1A, an optimal right atrial to right ventricleinterval is determined. However, in other embodiments, the leftatrial-left ventricular interval is optimized based on LV wall motion toensure optimal filling of the LV. A method for determining an optimalA-V interval based on LV wall motion will be described in conjunctionwith FIG. 5. At step 215, the A-V interval is automatically adjusted tothe optimal A-V interval determined at step 210.

[0050] At step 220, the optimal V-V interval is determined forbi-ventricular or atrio-biventricular pacing modes. A method foroptimizing the V-V interval based on LV wall motion will be described inconjunction with FIG. 7. At step 225, the V-V interval is automaticallyadjusted to the optimal V-V interval determined at step 220. Afteradjusting the V-V interval, an optional step 230 may be performed tore-optimize the A-V interval. Verification of the provisionallydetermined optimal A-V interval is made by re-determining the optimalA-V interval during biventricular pacing at the newly optimized V-Vinterval. The A-V interval may be re-adjusted accordingly if a differentA-V interval is identified as being optimal during pacing at the optimalV-V interval.

[0051]FIG. 5 is a flow chart summarizing steps included in a method fordetermining an optimal AV interval based on left ventricular wall motionfor use in method 200 of FIG. 4. Method 300 begins at step 305 bysetting the V-V interval to a nominal setting, preferably to 0 ms suchthat the left and right ventricles are paced simultaneously. At step 310an A-V test interval is set. A number of predetermined test A-Vintervals may be programmed. In a patient with intact atrioventricularconduction, the A-V intervals tested may include the intrinsic A-Vinterval. In order to allow intrinsic A-V conduction, the A-V intervalis set at a maximum setting or a setting longer than the intrinsic A-Vconduction time. The intrinsic A-V conduction time may be determined bymeasuring the interval from an atrial pacing pulse to a subsequentlysensed R-wave. Remaining test A-V intervals may be applied at decreasingincrements from the intrinsic A-V interval. Alternatively, test A-Vintervals may be applied randomly ranging from 0 ms to the intrinsic A-Vinterval. If atrioventricular conduction is not intact, a set of testA-V intervals may be selected over a predefined range, for example arange from 0 ms to on the order of 250 ms.

[0052] At step 315 a data collection window is set. LV wall motion datais preferably collected during systolic contraction such thatacceleration or motion of the left ventricular wall segment over whichthe wall motion sensor is positioned may be measured. However, LV wallmotion data may be acquired for use in assessing LV function oroptimizing a therapy during the isovolumic contraction phase, theejection phase, isovolumic relaxation, early diastolic filling, and/orlate diastolic filling. The data collection window may be a fixed timeinterval following a delivered ventricular or atrial pacing pulse (orsensed R-wave if intrinsic A-V conduction is being tested in patientswithout AV block). A data collection window may be set as a timeinterval beginning at the delivery of a ventricular pacing pulse with aduration on the order of 30 to 180 ms, for example.

[0053] At step 320, the LV wall motion signal is sampled during the datacollection window for each cardiac cycle during a predetermined timeinterval or for a predetermined number of cardiac cycles. In analternative embodiment, the LV wall motion signal may be acquiredcontinuously during the predetermined time interval or number of cardiaccycles and subsequently processed to separate components associated withthe maximum acceleration phase of the systolic contraction. The timeinterval or number of cardiac cycles preferably extends over at leastone respiration cycle such that averaging of the LV wall motion signalover a respiration cycle may be performed to eliminate variations in theLV wall motion measurements due to respiration. In one embodiment, thestart and stop of wall motion data acquisition may be triggered bysensing a respiration cycle. Respiration may be detected based onimpedance measurements or other methods known in the art.

[0054] At decision step 325, verification of a stable heart rate duringthe data acquisition interval is performed. Heart rate instability, suchas the presence of ectopic heart beats or other irregularities, wouldproduce anomalous LV wall motion data. As such, the heart ratepreferably stays within a specified range. In one embodiment, heart ratestability may be verified by determining the average and standarddeviation of the cardiac cycle length during the data acquisitionperiod. The cardiac cycle length may be determined as the intervalbetween consecutive ventricular events including ventricular pacingpulses and any sensed R-waves. If the average cardiac cycle length orits standard deviation falls outside a predefined range, the data isconsidered unreliable. Data acquisition may be repeated by returning tostep 315 until reliable data is collected for the current test intervalsetting.

[0055] At step 330, signal averaging is performed to minimize theeffects of respiration-related or other noise. The signals acquiredduring each cardiac cycle over the data collection interval are averagedto obtain an overall average LV wall motion signal. At step 340, one ormore signal features are determined from the averaged signal as ameasurement of LV wall motion and stored in device memory withcorresponding test interval information. Preferably, the maximumamplitude of an accelerometer signal or its maximum excursion determinedas the difference between the maximum and minimum peak amplitude, alsoreferred to herein as “peak-to-peak difference” is determined as ameasure of the maximum acceleration of the LV wall segment duringsystole. In one embodiment, the maximum peak amplitude or peak-to-peakdifference of an accelerometer signal during isovolumic contraction isused as a metric of LV function. Other LV wall motion signal featuresmay additionally or alternatively be determined as indices of LVmechanical function or hemodynamic correlates. Other LV wall motionsignal features that may be derived include, but are not limited to, aslope, an integral, a frequency component, or other time or frequencydomain characteristics.

[0056] If all test A-V intervals have not yet been applied, asdetermined at decision step 345, the method 300 returns to step 310 toadjust the A-V interval to the next test setting. Once all test A-Vintervals have been applied, the optimal A-V interval is identified fromthe stored LV wall motion data at step 350.

[0057]FIG. 6 is a graph of sample, experimental LV wall motion datacollected from an accelerometer during atrio-biventricular pacing atvarying A-V intervals and simultaneous right and left ventricular pacing(V-V interval set to 0 ms). As A-V interval is increased from 90 ms to200 ms, the maximum LV acceleration and peak-to-peak accelerationdecrease to a plateau point or “saddle point,” then increase again. Inone embodiment, the optimal A-V interval is selected as an A-V intervalcorresponding to the plateau or “saddle” point found by plotting aderived LV wall motion parameter as a function of A-V interval. In theexample shown in FIG. 6, the derived parameter is the peak-to-peakdifference of an accelerometer signal. Based on this parameter, and thecriteria described above, an optimal A-V interval can be identified as130 ms. Shorter A-V intervals can result in overlapping of left atrialand ventricular contraction and abrupt truncation of atrial contraction,resulting in an overall inefficient ejection of blood from theventricles and mitral valve regurgitation. Longer A-V intervals areundesirable because of fusion between the atrial and ventricular fillingphases of the cardiac cycle resulting in altered ventricular fillingpatterns. Reference is made to Leung SK et al., Pacing ClinElectrophysiol. 2000;23:1762-6.

[0058] When method 300 is executed by an external pacing system, LV wallmotion data may be displayed in real-time or stored and presentedfollowing an optimization procedure. When method 300 for identifying anoptimal A-V interval is executed by an implanted device, LV wall motiondata may be stored for later uplinking to an external device for displayand review by a physician. After identifying the optimal A-V interval,the A-V interval setting may be automatically adjusted according tomethod 200 described above.

[0059]FIG. 7 is a flow chart summarizing steps included in a method fordetermining an optimal V-V interval based on left ventricular wallmotion for use in method 200 of FIG. 4. At step 405, the A-V interval isprogrammed to an optimal setting determined according to method 300 ofFIG. 4. At step 410, the V-V interval is set to a test interval. A rangeof test intervals are predefined and may be delivered in a random,generally increasing, or generally decreasing fashion. A range of testintervals may include intervals that result in the right ventricle beingpaced prior to the left ventricle and intervals that result in the leftventricle being paced prior to the right ventricle. A set of exemplarytest intervals includes right ventricular pacing 20 ms and 40 ms priorto left ventricular pacing, simultaneous left and right ventricularpacing (a V-V interval of 0 ms), and left ventricular pacing 20 ms and40 ms prior to the right ventricle.

[0060] Method 400 proceeds to determine the optimal V-V interval in amanner similar to method 300 for determining the optimal A-V intervaldescribed above. A data collection window is set at step 415, and LVwall motion data is collected for a predetermined time interval ornumber of cardiac cycles at step 420 during the data collection windowapplied to each cardiac cycle. After verifying a stable heart rate atstep 425, signal averaging is performed at step 430 allowing an averagepeak amplitude or average peak-to-peak difference or other signalcharacteristic to be determined at step 435. After all test V-Vintervals are applied as determined at decision step 440, the optimalV-V interval is identified at step 445.

[0061]FIG. 8 is a graph of sample, experimental LV wall motion datacollected from an accelerometer during atrio-biventricular pacing atvarying V-V intervals and an A-V interval previously optimized to 130ms. Simultaneous right and left ventricular pacing occurs at a V-Vinterval of 0 ms. A convention of negative V-V intervals indicates theleft ventricle is paced earlier than the right ventricle, and positiveV-V intervals indicates right ventricular pacing occurs earlier thanleft ventricular pacing. In one embodiment, the optimal V-V interval isselected as the interval producing the maximum LV wall segmentacceleration based on the maximum peak amplitude, peak-to-peakdifference, or based on a fiducial point of an accelerometer signal. Inthe example shown, the optimal V-V interval may be identified, based onmaximum LV acceleration, as a 40 ms interval with the right ventriclepaced first and the left ventricle paced second.

[0062] When method 400 is executed by an external pacing system, LV wallmotion data may be displayed in real-time or stored and presentedfollowing an optimization procedure. When method 400 for identifying anoptimal V-V interval is executed by an implanted device, LV wall motiondata may be stored for later uplinking to an external device for displayand review by a physician. After identifying the optimal V-V interval,the V-V interval setting may be automatically adjusted according tomethod 200 described above.

[0063] As noted previously, after adjusting the V-V interval to anoptimal setting, verification that the A-V interval is still optimal maybe desired (step 230, FIG. 4). In order to re-optimize the A-V interval,method 300 may be performed as described above with the V-V intervalprogrammed to the optimal setting identified by method 400 rather than anominal setting. If a different A-V interval is found to be optimal, theA-V interval setting may be adjusted appropriately.

[0064] It is contemplated that optimization of A-V and V-V intervalsbased on LV wall motion according to the methods above may be performedin conjunction with an assessment of other wall segment motion, such asthe RV apex. In particular, it may be desired to verify that other wallsegment motion has not been degraded due to optimization of LV wallmotion. It may also be desirable to optimize one or more pacingintervals based on LV wall motion and other pacing intervals based on RVapical wall motion or the motion of other wall segments.

[0065]FIG. 9 is a flow chart summarizing steps included in a method formonitoring left ventricular function based on lateral wall motion. Asindicated previously, evaluation of left ventricular function is ofinterest for both diagnostic and therapeutic applications. Thus, it isrecognized, that aspects of the present invention may be employed formonitoring purposes without optimization of a therapy delivery. As such,method 500 summarized in FIG. 9 may be implemented in an implantable orexternal device, such as the devices those shown in FIGS. 1A, 1B andFIG. 3, for monitoring LV function by deriving and storing an LV wallmotion parameter from a sensed LV wall motion signal. The therapydelivery functions of such devices may be selectively disabled or, ifenabled, the optimization of cardiac pacing intervals based on LV wallmotion may be selectively enabled or disabled. Method 500 mayalternatively be implemented in internal or external devices that do notinclude therapy delivery capabilities, but in association with an LVlead equipped with a wall motion sensor, are capable of processing andstoring LV wall motion data.

[0066] LV wall motion may be sensed during a selected phase of thecardiac cycle on a continuous, periodic or triggered basis with the wallmotion signal characteristic determined and stored after eachpredetermined interval of time or number of cardiac or respiratorycycles. For example, LV function may be evaluated on a periodic basissuch as hourly, daily, weekly, or otherwise. Additionally oralternatively, LV function may be evaluated on a triggered basis, whichmay be a manual or automatic trigger. Automatic triggers may be designedto occur upon the detection of predetermined conditions during which LVfunction evaluation is desired, such as a particular heart rate range,activity, or other conditions.

[0067] In one embodiment, LV wall motion is monitored continuously andstorage of LV wall motion data is triggered upon the detection ofpredetermined data storage conditions, such as, but not limited to, aheart rate, activity, or a condition relating to LV wall motion. Forexample, LV wall motion may be sensed continuously, and, if an LV wallmotion parameter crosses a threshold or satisfies other predetermineddata storage criteria, LV wall motion parameter(s) are stored.

[0068] Manual triggers for LV wall motion sensing and/or data storagemay be delivered by a clinician or by a patient, for example when thepatient feels symptomatic. Methods for manually triggering the storageof physiological data in an implantable device are generally describedin U.S. Pat. No. 5,987,352 issued to Klein, et al., hereby incorporatedherein by reference in its entirety.

[0069] Method 500 begins at step 501 when LV wall motion sensing isenabled according to the mode of operation of the monitoring device,which as just described, may be continuous, periodic, automatically-and/or manually-triggered monitoring. At step 505, an LV wall motiondata collection window is set as described previously. At step 510, LVwall motion data is acquired for a predetermined interval of time ornumber of cardiac or respiratory cycles. At step 515, heart ratestability is verified as described previously. The wall motion signal isaveraged over the number of cardiac cycles collected at step 520 tominimize respiratory or other noise. At step 525, a characteristic ofthe averaged signal is determined and stored as an indication of LVfunction. Other physiologic or parametric data may be stored with the LVfunction data such as heart rate, date and time of day, pacing modalityand parameters, and/or any other physiological data that may be sensedby the monitoring device such as patient activity, blood pressure, etc.

[0070] When method 500 is implemented in an implantable device, storeddata are available through uplink telemetry to an external device forlater display and review by a physician. When method 500 is implementedin an external device, a display of LV function data may be updated eachtime an LV wall motion signal characteristic is determined.

[0071] Thus a method and apparatus have been described for monitoringleft ventricular cardiac contractility and optimizing a cardiac therapybased on left ventricular lateral wall acceleration measured using aleft ventricular lead equipped with an acceleration sensor. The methodsdescribed herein may advantageously be applied in numerous cardiacmonitoring or therapy modalities including chronic or acute applicationsassociated with implantable or external devices.

[0072] As is known in the art, besides the transducers describedhereinabove, other types of transducers may be used provided, ingeneral, that such transducers are hermetically sealed, are fabricated(on least on the exterior surfaces) of substantially biocompatiblematerials and appropriately dimensioned for a given application. Withrespect to appropriate dimension, a transducer intended to transvenousdeployment should be susceptible of catheter or over-the-wire delivery.Thus, the radial dimension should be on the order of less than about 11French and preferably about less than eight French. Also, the transducershould be somewhat supple, and not too long, in the longitudinaldimension so that the transducer can safely navigate the venous system,pass through the coronary sinus and enter vessels branching from thecoronary sinus (e.g., the great cardiac vein, and the like). Thesedimensions can be relaxed for a transducer intended for deploymentthough a portion of the chest (e.g., a thoracotomy) with an affixationmechanism adapted to mechanically couple adjacent the lateral wall. Twoadjacent locations include the epicardium and the pericardium. Thedimensions may be relaxed to a greater extent if the epicardial receivesthe transducer, and to a lesser extent, to a portion of the pericardium.As is well known, the pericardium is the membranous sac filled withserous fluid that encloses the heart and the roots of the aorta andother large blood vessels. One example of appropriate fixation apparatusfor epicedial application is a helical tipped lead that is screwed intothe surface of the epicardium. For pericardial fixation a sealing member(e.g., compressible gasket or opposing members on each side of thepericardial sac) may be used in addition to an active fixation membersuch as a helical tipped lead.

[0073] As is also known in the art related to sensors and transducers,accelerometers can be described as two transducers, a primary transducer(typically a single-degree-of-freedom vibrating mass which converts theacceleration into a displacement), and a secondary transducer thatconverts the displacement (of a seismic mass) into an electric signal.Most accelerometers use a piezoelectric element as a secondarytransducer. Piezoelectric devices, when subjected to a strain, output avoltage proportional to the strain, although piezoelectric elementscannot provide a signal under static (e.g., constant acceleration)conditions. Important characteristics of accelerometers include range ofacceleration, frequency response, transverse sensitivity (i.e.sensitivity to motion in the non-active direction), mounting errors,temperature and acoustic noise sensitivity, and mass.

[0074] One type of primary transducer, which describe the internalmechanism of the accelerometer, include spring-retained seismic mass. Inmost accelerometers, acceleration forces a damped seismic mass that isrestrained by a spring, so that it moves relative to the casing along asingle axis. The secondary transducer then responds to the displacementand/or force associated with the seismic mass. The displacement of themass and the extension of the spring are proportional to theacceleration only when the oscillation is below the natural frequency.Another accelerometer type uses a double-cantilever beam as a primarytransducer which can be modeled as a spring-mass-dashpot, only theseismic mass primary transducer will be discussed.

[0075] Types of secondary transducers, which describe how the electricsignal is generated from mechanical displacement, include:piezoelectric, potentiometric, reluctive, servo, strain gauge,capacitive, vibrating element, etc. These are briefly described as anintroduction for the uninitiated.

[0076] Piezoelectric transducers are often used in vibration-sensingaccelerometers, and sometimes in shock-sensing devices. Thepiezoelectric crystals (e.g., often quartz or ceramic) produce anelectric charge when a force is exerted by the seismic mass under someacceleration. The quartz plates (two or more) are preloaded so that apositive or negative change in the applied force on the crystals resultsin a change in the electric charge. Although the sensitivity ofpiezoelectric accelerometers is relatively low compared with other typesof accelerometers, they have the highest range (up to 100,000 g's) andfrequency response (over 20 kHz).

[0077] Potentiometric accelerometers utilize the displacement of thespring-mass system linked mechanically to a wiper arm, which moves alonga potentiometer. The system can use gas, viscous, magnetic-fluid, ormagnetic damping to minimize acoustic noise caused by contact resistanceof the wiper arm. Potentiometric accelerometers typically have afrequency range from zero to 20-60 Hz, depending on the stiffness of thespring, and have a high-level output signal. They also have a lowerfrequency response than most other accelerometers, usually between 15-30Hz.

[0078] Reluctive accelerometers use an inductance bridge, similar tothat of a linear variable differential transducer to produce an outputvoltage proportional to the movement of the seismic mass. Thedisplacement of the seismic mass in inductance-bridge accelerometerscauses the inductances of two coils to vary in opposing directions. Thecoils act as two arms of an inductance bridge, with resistors as theother two arms. The AC output voltage of the bridge varies with appliedacceleration. A demodulator can be used to convert the AC signal to DC.An oscillator can be used to generate the required AC current when a DCpower supply is used, as long as the frequency of the AC signal is fargreater than that of the frequency of the acceleration.

[0079] In servo accelerometers, acceleration causes a seismic mass“pendulum” to move. When motion is detected by a position-sensingdevice, a signal is produced that acts as the error signal in theclosed-loop servo system. After the signal has been demodulated andamplified to remove the steady-state component, the signal is passedthrough a passive damping network and is applied to a torquing coillocated at the axis of rotation of the mass. The torque developed by thetorquing coil is proportional to the current applied, and counteractsthe torque acting on the seismic mass due to the acceleration,preventing further motion of the mass. Therefore, the current throughthe torquing coil is proportional to acceleration. This device can alsobe used to measure angular acceleration as long as the seismic mass isbalanced. Servo accelerometers provide high accuracy and a high-leveloutput at a relatively high cost, and can be used for very low measuringranges (well below 1 g).

[0080] Strain gauge accelerometers, often called “piezoresistive”accelerometers, use strain gauges acting as arms of a Wheatstone bridgeto convert mechanical strain to a DC output voltage. The gauges areeither mounted to the spring, or between the seismic mass and thestationary frame. The strain gauge windings contribute to the springaction and are stressed (i.e., two in tension, two in compression), anda DC output voltage is generated by the four arms of the bridge that isproportional to the applied acceleration.

[0081] These accelerometers can be made more sensitive with the use ofsemiconductor gauges and stiffer springs, yielding higher frequencyresponse and output signal amplitude. Unlike other types ofaccelerometers, strain gauge accelerometers respond to steady-stateaccelerations.

[0082] In a capactivie accelerometer a change in acceleration causes achange in the space between the moving and fixed electrodes of acapacitive accelerometer. The moving electrode is typically adiaphragm-supported seismic mass or a flexure-supported, disk-shapedseismic mass. The element can act as the capacitor in the LC or RCportion of an oscillator circuit. The resulting output frequency isproportional to the applied acceleration.

[0083] In a vibrating element accelerometer, a very small displacementof the seismic mass varies the tension of a tungsten wire in a permanentmagnetic field. A current through the wire in the presence of themagnetic field causes the wire to vibrate at its resonant frequency(like a guitar string). The circuitry then outputs a frequencymodulation (deviation from a center frequency) that is proportional tothe applied acceleration. Although the precision of such a device ishigh, it is quite sensitive to temperature variations and is relativelyexpensive.

[0084] Thus, those of skill in the art will recognize that while thepresent invention has been described herein in the context of specificembodiments, it is recognized that numerous variations of theseembodiments may be employed without departing from the scope of thepresent invention. The descriptions provided herein are thus intended tobe exemplary, not limiting, with regard to the following claims.

1. A method for monitoring left ventricular function, comprising:deploying a motion sensor to a fixed location relative to a portion of aleft ventricular lateral wall wherein motion the sensor generates amotion signal proportional to motion of the lateral wall; opening a datacollection window during a portion of a selected cardiac cycle phase;storing the motion signal throughout at least a part of the portion ofthe data collection window for a predetermined time interval or for morethan one cardiac cycle; verifying a stability characteristic of themotion signal during the predetermined time interval or for more thanone cardiac cycle; averaging the stored motion signal; and determining asignal characteristic from the averaged stored signal that isrepresentative of left ventricular function.
 2. A method according toclaim 1, wherein said motion sensor is adapted to be disposed in aportion of the coronary sinus vessel or a blood vessel fluidly coupledto said coronary sinus.
 3. A method according to claim 2, wherein saidmotion sensor comprises an accelerometer.
 4. A method according to claim3, wherein the accelerometer comprises a uniaxial accelerometer having alongitudinal sensing axis substantially aligned toward the leftventricular apex portion of the heart.
 5. A method according to claim 2,wherein said motion sensor comprises a biaxial accelerometer.
 6. Amethod according to claim 2, wherein said motion sensor comprises atriaxial accelerometer.
 7. A method according to claim 1, wherein saidmotion sensor is adapted to be disposed adjacent to a portion of theepicardium of the left ventricle of the heart.
 8. A method according toclaim 7, wherein the portion of the epicardium is a portion of thelateral wall of the left ventricle.
 9. A method according to claim 8,wherein the portion of the lateral wall is a basal portion of thelateral wall.
 10. A method according to claim 9, wherein the portion ofthe lateral wall is a mid-basal portion of the lateral wall.
 11. Amethod according to claim 1, wherein said motion sensor is adapted to bedisposed within the pericardium of the heart.
 12. A method according toclaim 3, wherein the device comprises an implantable medical device. 13.A method according to claim 12, wherein the first pacing electrode orthe second pacing electrode further comprises a sense electrode inelectrical communication with a sensing circuit coupled to the device.14. A computer readable medium programmed with instructions forperforming a method for assessing left ventricular function andoptimizing cardiac pacing intervals in a device programmed to operate abi-ventricular cardiac pacing modality, comprising: instructions forsensing movement of a portion of a left ventricular chamber of a heartwith a deployed movement transducer and for measuring a motion signalfrom the transducer related to the movement; instructions for opening adata collection window during a portion of a selected cardiac cyclephase; instructions for storing the motion signal throughout at least apart of the portion of the data collection window for a predeterminedtime interval or for more than one cardiac cycle; instructions froverifying a stability characteristic of the motion signal during thepredetermined time interval or for more than one cardiac cycle;instructions for averaging the stored motion signal; and instructionsfor determining a signal characteristic from the averaged stored signalthat is representative of left ventricular function.
 15. A computerreadable medium according to claim 14, wherein said motion sensor isadapted to be disposed in a portion of the coronary sinus vessel or ablood vessel fluidly coupled to said coronary sinus.
 16. A computerreadable medium according to claim 15, wherein said motion sensorcomprises an accelerometer.
 17. A computer readable medium according toclaim 16, wherein the accelerometer comprises a uniaxial accelerometerhaving a longitudinal sensing axis substantially aligned toward the leftventricular apex portion of the heart.
 18. A computer readable mediumaccording to claim 15, wherein said motion sensor comprises a biaxialaccelerometer.
 19. A computer readable medium according to claim 15,wherein said motion sensor comprises a triaxial accelerometer.
 20. Acomputer readable medium according to claim 14, wherein said motionsensor is adapted to be disposed adjacent to a portion of the epicardiumof the left ventricle of the heart.
 21. A computer readable mediumaccording to claim 20, wherein the portion of the epicardium is aportion of the lateral wall of the left ventricle.
 22. A computerreadable medium according to claim 21, wherein the portion of thelateral wall is a basal portion of the lateral wall.
 23. A computerreadable medium according to claim 22, wherein the portion of thelateral wall is a mid-basal portion of the lateral wall.
 24. A computerreadable medium according to claim 14, wherein said motion sensor isadapted to be disposed within the pericardium of the heart.
 25. Acomputer readable medium according to claim 16, wherein the devicecomprises an implantable medical device.
 26. A computer readable mediumaccording to claim 25, wherein the first pacing electrode or the secondpacing electrode further comprises a sense electrode in electricalcommunication with a sensing circuit coupled to the device and furthercomprising: instructions for measuring depolarization wave activity andat least temporarily storing at least one parameter related to themeasured depolarization wave activity.
 27. A method for optimizingcardiac pacing intervals based on left ventricular function, comprising;placing a motion sensor into electromechanical communication with a leftventricular lateral free wall so that the motion sensor generates amotion signal proportional to the motion of the lateral free wall;enabling a temporal data collection window corresponding to a selectedcardiac cycle phase; applying a cardiac pacing stimulus deliveredaccording to a preselected set of test pacing parameters; sensing themotion signal during at least a part of the temporal data collectionwindow or during a more than one cardiac cycle for at least some membersof the preselected set of test pacing parameters; verifying a heart ratestability condition; averaging the motion signal for the at least somemembers of the preselected set of test pacing parameters; determining asignal characteristic from the averaged sensed signal that isrepresentative of relatively improved left ventricular function duringeach of the selected test pacing parameters; and storing a cardiacpacing timing parameter for a right ventricular pacing electrode and fora left ventricular pacing electrode that resulted in the relativelyimproved left ventricular function.
 28. An apparatus for optimizing leftventricular function, comprising: means for sensing motion of a portionof the left ventricle and providing a motion signal; means forstimulating a left ventricle and a right ventricle at the same momentand at different moments; means for storing the sensed motion signalsduring a temporal window when the left ventricle and the right ventricleare stimulated at the same moment and at different moments; means forconfirming that a stability condition for the left ventricle and theright ventricle exists; means for mathematically averaging the sensedmotion signals for corresponding to when left ventricle and the rightventricle are stimulated at the same moment and at select differentmoments; means for determining a signal characteristic from the averagedsensed motion signals that represents a relatively improved leftventricular function; and means for storing a cardiac pacing timingparameter for a right ventricular pacing electrode and for a leftventricular pacing electrode that resulted in the relatively improvedleft ventricular function.
 29. A method according to claim 28, whereinsaid means for sensing motion comprises a motion sensor adapted to bedisposed in a portion of the coronary sinus vessel or a blood vesselfluidly coupled to said coronary sinus.
 30. A method according to claim29, wherein said motion sensor comprises an accelerometer.
 31. A methodaccording to claim 30, wherein the accelerometer comprises a uniaxialaccelerometer having a longitudinal sensing axis substantially alignedtoward the left ventricular apex portion of the heart.
 32. A methodaccording to claim 29, wherein said motion sensor comprises a biaxialaccelerometer.
 33. A method according to claim 29, wherein said motionsensor comprises a triaxial accelerometer.
 34. A method according toclaim 28, wherein said means for sensing motion is adapted to bedisposed adjacent to a portion of the epicardium of the left ventricleof the heart.
 35. A method according to claim 34, wherein the portion ofthe epicardium is a portion of the lateral wall of the left ventricle.36. A method according to claim 35, wherein the portion of the lateralwall is a basal portion of the lateral wall.
 37. A method according toclaim 26, wherein the portion of the lateral wall is a mid-basal portionof the lateral wall.
 38. A method according to claim 28, wherein saidmotion sensor is adapted to be disposed within the pericardium of theheart.
 39. A method according to claim 30, wherein the device comprisesan implantable medical device.
 40. A method according to claim 39,wherein the first pacing electrode or the second pacing electrodefurther comprises a sense electrode in electrical communication with asensing circuit coupled to the device.